A vibratory gyroscope system is comprised of a sensor (gyroscope) that is used to sense rotation of some inertial mass with respect to a frame of reference, and some support circuitry. Operation of a vibratory gyroscope is based on the Coriolis effect. As such, the gyroscope has two orthogonal axes. Generally speaking, an inertial mass is driven to have some velocity along the first axis; further, the mass is typically a resonant structure and so this axis will be referred to as the Resonator axis. Due to the Coriolis effect, when the mass is rotated with respect to an observational reference frame, there will be a Coriolis force exerted along the second axis. The second axis is referred to as the Coriolis axis. The effect of the force on the Coriolis axis can be sensed and rotation can be calculated.
The support circuitry provides at least two functions. First, the support circuitry drives the mass into motion along the resonator axis. This circuitry, along with the gyroscope, is referred to as the Resonator Signal Path (RSP) or simply as the resonator. Second, the support circuitry senses a signal along the Coriolis axis. This circuitry, along with the gyroscope, is referred to as the Coriolis Signal Path (CSP) or as the accelerometer.
Many current vibratory gyroscopes use open-loop CSP and closed-loop RSP for robust sensitivity. This leaves the system sensitive to the quality factor of the gyroscope along the Coriolis axis. Then, the Resonator and Coriolis modes are intentionally split in frequency, so that the excitation of the Coriolis axis is off-resonance and the response is stable even in the presence of variation of the Coriolis axis Q. This approach works for low-Q resonators, when the mode split can be done at the factory and stays stable enough with life. For high-Q gyroscopes, this is not an acceptable solution, as the reduction in Q due to mode-splitting would undo the benefits of using a high-Q structure. Another solution would be to calibrate the Sensitivity over temperature. However, this is expensive, e.g., involving a multi-pass Automatic Test Equipment (ATE) test, and is less reliable.